The manufacture of electronic components, such as semiconductor wafers, liquid crystal displays, light emitting diodes and solar cells typically requires nitrogen containing ten parts per billion (ppb) or less of several contaminants, including carbon monoxide, hydrogen, and oxygen. Nitrogen containing contaminants at these levels is referred to as ultra-high purity nitrogen. Ultra-high purity nitrogen is used, for example, to generate a contaminant-free atmosphere during various electronic component processing steps, thereby minimizing the number of defects in the product manufactured.
The base material utilized in the production of ultra-high purity nitrogen is air. Although the system is described with reference to nitrogen, any number of gases such as helium, hydrogen, oxygen, argon and rare gases may be employed. With reference to FIG. 1, a conventional system 100 is depicted. Air is introduced into compressor 110 where it is compressed to a pressure ranging from 35 psig to 200 psig. The resulting high pressure air stream is fed to an adsorption system 120, which contains two or more beds arranged in parallel. Adsorption system 120 typically operates at or near ambient temperature and removes high boiling point contaminants such as water and carbon dioxide. The resulting purified air is routed to a cryogenic air separation unit 130 that contains, for example, at least one distillation column and removes the preponderance of moderate boiling point contaminants such as oxygen. The nitrogen stream which exits the air separation unit is a conventional purity nitrogen stream and typically contains 1-10 parts per million (ppm) oxygen, 1-10 ppm carbon monoxide and 1-10 ppm hydrogen. The air separation unit also produces an oxygen-containing stream that may be utilized in part to remove contaminants from adsorption system 120.
The conventional purity nitrogen stream is further purified in chemical adsorption based gas purifier 140. This gas purifier typically contains a chemical adsorbent that is based on a metal, such as nickel, and reacts with and/or adsorbs any residual oxygen, hydrogen and carbon monoxide. Contaminants that have reacted with or adsorbed on the metal based catalyst are removed in a regeneration step by reaction and thermal desorption using a heated hydrogen/ultra-high purity nitrogen mixture. Typically, 1-10% of the ultra-high purity nitrogen stream is employed for this purpose. The nitrogen/hydrogen/contaminant mixture exiting the chemical adsorption based purification system 140 is discarded.
The ultra-high purity nitrogen stream generated in the purifier is then routed to filter system 150 to remove any particulates, and thereafter the ultra-high purity nitrogen stream is routed to the point of use.
The conventional purity nitrogen stream exiting the air separation unit 130 can be compromised, for example, by air entering the system, before the stream reaches the gas purifier 140. A high concentration of some contaminants/impurities, such as oxygen, can create an exothermic reaction. As a result, the chemical adsorbent in gas purifier 140 reaches temperatures exceeding a predetermined value, typically ranging between 120° F. and 400° F. In this situation, the gas purifier 140 is taken off-line and ultra-high purity nitrogen flow to the end user is discontinued. Because the end user does not receive ultra-high purity nitrogen when this occurs, a substantial economic loss is incurred.
Various attempts have been made to monitor the temperature in the gas purifier, so as not to allow the chemical adsorbent to exceed a specified temperature. Lorimer et al in U.S. Pat. Nos. 6,068,685; 6,156,105; 6,232,204; and 6,398,846 disclose a gas purifier including a getter column having a metallic vessel and a containment wall extending between the inlet and the outlet. The getter material purifies gas flowing therethrough by adsorbing impurities therefrom. A first temperature sensor is located in the top portion of the getter material and a second temperature sensor is located in the bottom portion of the getter material to rapidly detect the onset of an exothermic reaction which indicates the presence of excessive impurities in the gas which is to be purified.
Christel, Jr. et al in U.S. Pat. No. 4,832,711 describes a system for adsorbing water vapor from a mixture thereof with a second gas to reduce the water vapor or first gas concentration in the mixture to below a permissible maximum concentration by sensing the advance of the temperature front that precedes the adsorption front.
Harrison in U.S. Pat. No. 4,816,043 discloses the selective separation or fractionation of components from a fluid or gas mixture, for example, water from a pressurized air stream, using a desiccant. The remaining desiccant capacity is determined by sensing the advance of the temperature front that precedes the adsorption front.
It is increasingly desirable to design a gas purifier system in which equipment failure (i.e., temperature sensor, computer card, etc.) is distinguished from a real event (i.e., exothermic reaction within the purifier) which would necessitate the isolation of the purifier, and in turn discontinuation of the supply of purified gas to the end user.